A 50-mile stretch of Interstate 15 in Nevada remained closed Tuesday after flash flooding in the desert Southwest left a trail of damage from Tucson to Las Vegas, including at least two deaths in Arizona.

Nevada state officials ordered the I-15 closed between about 30 miles north of Las Vegas and the Utah state line, after as much as 4 inches of rain pounded the area during a two-hour period Monday and left the roadway buckled and...